Synthesis of glycidyl ethers of polyhydric phenols



United States Patent 3,121,727 SYNTHESIS OF GLYCBDYL ETHERS 0FPOLYHYDRIC PHENOLS John J. Baliker, In, Kenneth B. Cofer, and Leonard H.Grifiin, Pasadena, and Dwight M. Sheets, Houston, Tex., assignors toShell Oil Company, New York, N.Y., a corporation of Delaware No Drawing.Filed Oct. 17, 1960, Ser. No. 62,853 2 Claims. (Cl. 26t)-34i8.6)

This invention relates to an improved process for the manufacture ofglycidyl ethers of polyhydric phenols. More particularly it relates toimprovements in reaction rate and product purity in the manufacture ofsuch glycidyl ethers.

Glycidyl polyethers of polyhydric phenols, often termed epoxy resins,are valuable materials which are used in many applications such assurface coatings, adhesives, molding compositions, and the like. Theyare generally prepared by reacting a polyhydric phenol withepichlorohydrin in an alkaline medium. A particularly versatile group ofepoxy resins are manufactured from epichlorohydrin and a dihydric phenolsuch as 2,2-bis(4-hydroxyphenyl)propane, often called p,p'-bisphenol Aor simply bisphenol A. The predominant constituent of these polyethersmay be represented by the formula wherein n is an integer of the series0, 1, 2, 3, etc. and R represents the divalent radical to which the twophenolic hydroxy groups are attached in the dihydric phenol. The molratio of epichlorohydrin to dihydric phenol employed in preparing theresin is the most important factor in controlling the average molecularweight of the polyether and hence the average value of n. Certain usesof epoxide resins require that they have a particular average value ofn. Thus, for adhesive application it is desirable that average n closelyapproach zero. The present invention is particularly directed to theproduction of compounds having a predominant proportion of thediglycidyl ether of the bisphenol, i.e., those compounds in which n iszero.

In the best processes heretofore known for the commercial production ofdigylcidyl ether of bisphenyl A it was found that the reaction ratelimits the amount of time required for completion of the reactionbetween bisphenol A and epichlorohydrin. It was further found thatbecause of the relatively long reaction times required, i.e. severalhours, a significant amount of by-products other than a diglycidyl etherwas made, including compounds which retain chlorine even after theconventional dehydrochlorination has been completed. In the commercialproduction of diglycidyl ether and bisphenol A by methods heretofore inuse a reaction time of 2 to 3 hours is usually required for completionof caustic addition and the best product which can be made fromingredients of commercial purity contains total chlorine of the order of0.3% by weight and saponifiable chlorine of the order of 0.1% wt. ormore.

It is an object of this invention to provide an improved method forcarrying out the production of glycidyl ethers of polyhydric phenols. Itis a specific object to provide an improved method for the industrialproduction of diglycidyl ether of p,p'-bisphenol A. Another specificobject is to provide a method for the industrial production ofdiglycidyl ether of p,p=-bisphenol A in which the reaction time is inthe range from minutes to 1 hour and in which the resulting product hasa very low content of total chlorine and of saponifiable chlorine. Otherobjects will be apparent from the following description of thisinvention.

According to this invention glycidyl ether of a polyhydric phenol isproduced by adding an aqueous solution of alkali metal hydroxidecontaining at least 15% by weight of the hydroxide to an agitatedsolution of a polyhydric phenol in at least about 3 mols ofepichlorohydrin per phenolic hydroxyl equivalent of the phenol and asuflicient amount of methanol to maintain a single liquid phase untilreaction is complete. The addition of said hydroxide solution iscontrolled at a rate which permits removal of heat of reaction byremoving a vapor stream from the reaction mixture at approximatelyatmospheric pressure, condensing said vapor stream and returning thecondensate to the reaction.

The chemical reactions involved in producing the glycidyl ethers ofpolyhydric phenols and the various phenols which can be used asreactants are described in some details in US. 2,801,227 to Goppel,which is incorporated herein by reference to avoid unnecessaryrepetition of subject matter already well known to the art. For purposesof explaining the present invention it is sufiicient to discuss theproduction of the diglycidyl ether of 2,2-bis(4-hydroxyphenyl)propane.it will be understood that the reaction can be carried out with otherphenols such as those enumerated by Goppel.

The method described by Goppel is a useful commercial method for theproduction of epoxy resins. It will be noted, however, that in a typicalprocess according to that method (Example I) the time required foraddition of aqueous sodium hydroxide was 3% hours, the reactiontemperature was between 210 and 246 F. and the product obtained had anepoxy value of 0.519 epoxy equivalents per grams (which corresponds to aweight per epoxide of 193) and contained 0.52% chloride.

By contrast, in the process of this invention the reaction is completedin a period from 10 to 15 minutes on laboratory scale and even inavailable commercial equipment in 30 minutes or less; the reactiontemperature is generally about to F.; and the resulting diglycidyl etherof bisphenol A has a weight per epoxide of about 180 and a totalchlorine content of about 0.2% or less.

In the methods heretofore employed, such as described for example in theGoppel patent, it has been necessary to maintain the concentration ofwater at a very low value, e.g., from about 0.3 to 2% by weight, duringthe course of reaction in order to avoid the formation of a second layerwith the resulting side reactions. in the process of the presentinvention the addition of methanol makes the water concentration muchless critical; much higher water concentrations can be tolerated. In theprocess of this invention, water removal is not necessary during thereaction step.

The process of this invention has permitted for the first time thedirect production of a concentrate of diglycidyl ether of bisphenol Awhich contains an extremely low proportion of total chlorine andsaponifiable chlorine without requiring resort to elaborate methods ofrecrystallization or redistillation. The process further has reduced thetime requirement for addition of caustic during the condensationreaction step from 2 hours or more to onehalf hour or less. This resultsin a very substantial increase in the capacity of existing commercialequipment or conversely, permits a substantial reduction in capitalrequired to build a plant of a given throughput capacity.

Although various solvents have been heretofore proposed for use in thecondensation of epichlorohydrin with polyhydric phenols, it has now beensurprisingly found that methanol has unique and unexpected advantages.Its use results in a very substantial increase in reaction rate as wellas a substantial reduction in chlorine content of the product. Althoughthis invention is not to be limited by any theoretical consideration, itis believed that the extreme polarity of methanol is a material factorin achieving the superior results. It results in a homogeneous solutionof epichlorohydrin and sodium phenolates. The homogeneous system favorsthe condensation to form the glycidyl ether. If a separate aqueous phasewere to form during the reaction, the amount of by-product due to sidereactions of the epichlorhydrin would become very substantial, resultingin impure product as well as in the loss of epichlorohydrin.

The process of this invention is suitably executed in a reaction vesselequipped with a mechanical stirrer, a valved inlet for feeding aqueoushydroxide solution, means for measuring the temperature of the'reactionmixture, heating means, and a vapor outlet fitted with a condenser andvapor temperature measuring device. Condensed distillate from thecondenser is returned to the reactor.

In carrying out the process the reactor is charged with the dihydricphenol, epichlorohydrin, and methanol. At least a small amount of water,e.g., about 1 percent, based on epichlorohydrin is present in theinitial reaction mixture. When the reaction is initiated by the additionof aqueous caustic, the reaction mixture may be at ambient temperatureor at a moderately elevated temperature. The temperature of the reactionmixture rises as caustic is gradually added. Temperature control ismaintained by vaporization of light components from the reaction mixtureand reflux thereof. The rate of caustic addition is controlled to avoidaddition at a more rapid rate than that at which heat can be removed.After completion of the reaction, the reaction mixture is treated forrecovery of the desired glycidyl ether substantially in the mannerdescribed in the Goppel patent.

The temperature of the reaction mixture before caustic addition iscommenced may be ambient temperature. It is preferably moderatelyelevated, e.g., between about 130 and 150 F. and most preferably betweenabout 140 and 145 F. During the addition step the temperature rises,e.g., to a value in the range from 160 to 180 F. Correspondingly loweror higher temperatures are used if operations are carried out atsubatmospheric or superatmospheric pressure. However, the reaction isusually carried out at substantially atmospheric or slightlysuperatmospheric pressure, e.g., between and 2 p.s.i.g. For best resultsit is desired to maintain the reaction pressure at a value which resultsin a temperature not above 180 F.

It is important in the process of this invention that a substantialconcentration of methanol be present in the reactor at the initiation ofthe reaction. Useful results can generally be obtained with between and100%, but it is generally preferred to have to 50% methanol initiallypresent. At least sufficient methanol is required to maintain a singlereaction phase throughout the reaction. Obviously, more methanol isrequired for this purpose if it is desired to use a relatively diluteaqueous caustic than is required when a very concentrated aqueouscaustic is employed. For best results, the methanol concentration isgenerally maintained throughout the reaction period in the range betweenand by weight of methanol, based on the amount of epichlorohydrinpresent.

The presence of methanol in the stated concentration permits control ofthe reaction temperature at a relatively low value by virtue of methanolevaporation during caustic addition.

The vapor leaving the reaction mixture contains water, epichlorohydrinand methanol. The condensed vapor is not necessarily the equilibriumazeotrope since the boiling reaction mixture is relatively deficient inwater. By virtue of the presence of methanol in the condensate no phaseseparation takes place.

The epichlorohydrin employed in the process is not only a reactant butis also a solvent for the polyhydric phenol and the resulting glycidylether of the phenol. As has been explained, the addition of methanolmodifies the solution and permits the presence of substantial amounts ofwater without phase separation occurring. Usually the process isexecuted with use of about 3 to 8 mols of epichlorohydrin per phenolichydroxyl equivalent of the polyhydric phenol, and preferably with from 4to 6 mols. Large quantities can be used if desired, such as up to 6 molsor higher, but they give no particular advantage and are generally notemployed because it is essential that all unreacted epichlorohydrin berecovered as a matter of economy. When the phenol is dihydric, the usualrange is thus 6 to 16 mols epichlorohydrin per mol of phenol andpreferably 8 to 12 mols per mol.

The alkali metal hydroxide, such as sodium or potassium hydroxide, ispreferably added to the reaction mixture as an aqueous solution whichcontains at least about 15 by weight and may contain up to thesaturation concentration of the hydroxide. It is preferred to use arelatively concentrated solution of about 40% to 45% concentration.Ordinary 48 Be. commercial caustic soda is suitable.

The total amount of alkali metal hydroxide added is about 1 mol perphenolic hydroxy equivalent of the polyhydric phenol, i.e., about 2 molsper mol of dihydric phenol. This amount is suficient to combine with andneutralize the hydrogen chloride liberated by the reaction between theepichlorohydrin and the phenol. Rather than using exactly one mole it ispreferable to use a slight excess such as a 2% excess and in some casesup to 5% excess. Use of large excesses is avoided since this. causesloss of epichlorohydrin to unwanted by-products. It is often preferredto add slightly less than a molar equivalent, e.g., about 1.95 mol NaOHper mol bisphenol A, during the reaction step, and to add the remainder,including the slight excess, during the dehydrochlorination step.

A small amount of water is required for the condensation reaction totake place. Additional Water is formed during the condensation reactionand water is also added as part of the aqueous caustic. The amount ofwater originally present is preferably at least about 1% and may be upto 10% by weight of the reaction mixture. Depending on the conditionsused, the concentration of water may become as high as about 14% duringthe course of the reaction without resulting in phase separation.

The time required for the addition of caustic during the condensationstep in this process is not limited by the rate of reaction betweenepichlorohydrin and polyhydric phenol, but only by the rate at whichheat can be removed from the reaction system. This is one significantdifference between the process of this invention and those heretoforeknown. In the laboratory complete reaction has been obtained accordingto this invention in as little as 1 0 minutes and in commercialequipment 30 minutes is usually more than sufficient. Product of greaterpurity is obtained when caustic is added as rapidly as temperaturecontrol will permit and the reaction is discontinued after causticaddition is complete.

After completion of caustic addition any available method for recoveringand purifying the resin may be suitably employed. Such methods aredescribed in various patents and publications and are known to the art.It is important, however, that the preponderant amount of thesaponifiable chlorine remaining in the resin at the completion ofcaustic addition be removed by a dehydrochlorination reaction. Thefollowing describes a representative method of product workup.

Followng the completon of caustic addition, unreacted epichlorohydrinand the methanol and Water are removed from the reaction mixture. Thismay suitably be done by flash distillation at atmospheric pressure. Thesmall remaining amount of these low molecular weight ingredients maythen be removed by stabilizing the resin, e.g., by vacuum distillationsuch as distillation at 15 mm. Hg

5 absolute at 320 F. for 15 minutes. Alternatively, the remaining lightingredients may be removed by steam stripping.

The remaining product contains sodium chloride formed during thecondensation reaction. This may be removed in known manner, e.g., byadding methyl isobutyl ketone and water to result in a two phase systemin which the upper layer consists of a solution of the desireddiglycidyl ether in methyl isobutyl ketone and the lower layer consistsof an aqueous brine. The resin can be recovered by separating the upperlayer. The separated resin slution is then suitably treated with anequal volume of caustic at 190 F. for 1 hour to remove the remainingchlorine by a dehydrochlorination reaction. The resin solution is thenneutralized, e.g., by adding an equal volume of 3-4% aqueous monosodiumphosphate and removing the residual methyl isobutyl ketone by flashdistillation. The essentially solvent-free resin can then again bestabilized, e.g., by vacuum distillation at about mm. Hg and 340 F. for15 minutes. After filtering, the resulting product is a resin ofextremely high purity.

The invention may be better understood from the following illustrativeand comparative examples. The invention is not to be construed aslimited to the details described. Percentages and parts in the examplesand throughout the speification are by Weight, unless otherwiseindicated.

EXAMPLE 1 Ten parts of epichlorohydrin, 5 parts of methanol and 1 partof bisphenol A containing about 97% of the p,p' isomer are placed in astirred flask. 0.1 part of water is added and the mixture heated to 150F. 45% aqueous caustic at ambient temperature is then gradually addedover a period of 30 minutes. The total amount of caustic added is 1.95mols per mol of bisphenol A. The reaction temperature rises to theatmospheric boiling point of the mixture which is 162 F. Vapor distilledfrom the reaction vessel during the period of caustic addition iscondensed and returned to the reactor; no phase separation is observed.The water content of the reactor gradually rises to about 8%.

Following completion of caustic addition, excess epichlorohydrin, waterand methanol are removed from the crude resin by flash distillation atatmospheric pressure. The resin is then stabilized at 320 F. and about15 mm. Hg absolute for 15 minutes. Methyl isobutyl ketone and water areadded to yield a two-phase system consisting of a resin-methyl isobutylketone upper layer and a brine lower layer. The upper layer is separatedand batch dehydrochlorinated with an equal volume of 5% wt. caustic at190 F. for one hour. Following neutralization of the resin solution withan equal volume of 34% wt. aqueous monosodium phosphate and removal ofresidual methyl isobutyl ketone by flash distillation, the essentiallysolventfree resin is further stabilized at 320 F. and about 15 mm. Hgabsolute for 15 minutes and then filtered.

The resin produced in this experiment had a viscosity of 75 poises at 25C. and a molecular Weight per epoxide group of 184. The cure rate of theresin, determined in a standard fashion by observing the change inrefractive index with time, was 54 10 EXAMPLE 2 A series of experimentswere carried out in which the methanol concentration was :varied and thereaction temperature was permitted to vary accordingly, since allreactions were carried out at atmospheric pressure. Reaction time was 1hour, the water content rose during cautsic addition from 1 to 8% byweight, the epichlorohydrin to bisphenol A mol ratio was 10:1, thecaustic to bisphenol A mol ratio 1.95:1. The results are indicated inthe following Table 1.

Table 1 Reaction Conditions Resin Properties CHBOH Conecn- ReactionViscosity, Cure Rate, Weight tration, Tempera- Poises, ARIXIO per g./l00g. ECH ture, F. 25 C. Epoxide It is seen that the best results, asindicated by a low viscosity and a low weight per epoxide, were obtainedwith a methanol concentration of 20% based on epichlorohydrin at areaction temperature of 171 F. Results with 10 and 50% methanol, basedon epichlorohydrin, were still quite satisfactory. The extremeconcentrations of 5% and respectively, were substantially lesssatisfactory.

EXAMPLE 3 Although the above experiments were carried out at reactiontimes of 1 hour it was found that equally good results were obtainedwhen the reactions with methanol solvent present were repeated atreaction times of as little as 15 minutes.

EXAMPLE 4 Reactions were carried out similarly to Example 2 but using avariety of diiferent solvents. The results obtained with methanol,ethanol, isopropanol and acetone are illustrated in Table 2. Tht greatlysuperior results obtained with methanol are apparent from the fact itshowed the lowest weight per epoxide, a very much lower viscosity, and avery much lower content of total chlorine and of saponifiable chlorine,as well as much lower color.

When Example 1 is repeated with substitution of different phenols forthe bisphenol, similarly superior products are obtained. The phenolssubstituted in Example 1 are, for example, resorcinol, hydroquinone,4,4'-dihydroxyldiphenyl, bis-4-hydroxyphenyl methane and others.

We claim as our invention:

1. A process for the production of diglycidyl ether of2,2-bis(4-hydroxyphenyl) propane which comprises (A) adding aconcentrated aqueous solution of sodium hydroxide to an agitatedsolution containing (a) said phenol,

(b) from about 6 to about 16 mols of epichlorohydrin per mol of phenol,

(c) from 1 to 10 percent by weight of water, and

-(d) a sufficient amount of methanol in the range from 0.1 to 0.5 partby weight per part of epichlorohydrin, to maintain a single liquid phasethroughout the reaction;

(B) removing heat of reaction by removing a vapor stream from thereaction mixture, condensing said vapor stream, and returning thecondensate to the reactor;

(C) the rate of adding said solution of sodium hydroxide being such thatthe condensation reaction (3 6.) between said phenol and epichlorohydrinis complete References Cited in the file of this patent Within minutes,and (D) the rate of said heat removal being such that the UNITED STATESPATENTS htilat of reaction is removed from the reaction zone 2 739 160Bell et a1 Mar 20 1956 w ile maintaining the reaction mixture at itsboiling 5 2848435 u 1 point, and 11 net a. ug. 9, 1938 (E) recovering areaction product characterized by 2,898,349 ZuPPmger et all & a weightper epoxide group of about 180 to 184 and 2,932,626 Phillips 6t P 1960 atotal chlorine content of no more than about 0.2% 2,943,095 Farnham eta1. June 28, 19 by weight. 10 3,014,892 Schwarzer et al Dec. 26, 1961 2.The process according to claim 1 wherein said agi- 3,016,362 Wismer 1 91952 tated solution, prior to said addition of sodium hydroxide 3 033803 Price et 81 i May 1962 solution, is at a temperature of betweenabout and 3033816 P a t n N 1962 F. and the reaction temperature, afteraddition of i e my 3,033,819 Price et al. May 8, 1962 sodium hydroxidesolution has been initiated, is main- 15 tained in the range from to F.

1. A PROCESS FOR THE PRODUCTION OF DIGLYCIDYL ETHER OF2,2-BIS(4-HYDROXYPHENYL)PROPANE WHICH COMPRISES (A) ADDING ACONCENTRATED AQUEOUS SOLUTION OF SODIUM HYDROXIDE TO AN AGITATEDSOLUTION CONTAINING (A) SAID PHENOL, (B) FROM ABOUT 6 TO ABOUT 16 MOLSOF EPICHLOROHYDRIN PER MOL OF PHENOL, (C) FROM 1 TO 10 PERCENT BY WEIGHTOF WATER, AND (D) A SUFFICIENT AMOUNT OF METHANOL IN THE RANGE FROM 0.1TO 0.5 PART BY WEIGHT PER PART OF EPICHLOROHYDRIN, TO MAINTAIN A SINGLELIQUID PHASE THROUGHOUT THE REACTION; (B) REMOVING HEAT OF REACTION BYREMOVING A VAPOR STREAM FROM THE REACTION MIXTURE, CONDENSING SAID VAPORSTREAM, AND RETURNING THE CONDENSATE TO THE REACTOR; (C) THE RATE OFADDING SAID SOLUTION HYDROXIDE BEING SUCH THAT THE CONDENSATION REACTIONBETWEEN SAID PHENOL AND EPICHLOROPHYDRIN IS COMPLETE WITHIN 30 MINUTES,AND (D) THE RATE OF SAID HEAT REMOVAL BEING SUCH THAT THE HEAT OFREACTION IS REMOVED FROM THE REACTION ZONE WHILE MAINTAINING THEREACTION MIXING AT ITS BOILING POINT, AND (E) RECOVERING A REACTIONPRODUCT CHARACTERIZED BY A WEIGHT PER EPOXIDE GROUP OF ABOUT 180 TO 184AND A TOTAL CHLORINE CONTENT OF NO MORE THAN ABOUT 0.2% BY WEIGHT.